Octant

Octant

Exploration, navigation, technology

This is an image of an octant, which was a navigational instrument used during the 18th century. The octant is a reflective instrument (also known as a reflective quadrant), and was first developed by Sir Isaac Newton in 1699, but official credit has been given to Thomas Godfrey John Hadley, who developed their versions of the octant in the 1730s, due to the timing of the publication of the information. Reflective mirrors were criticial to the function of this instrument as it allowed for more accurate alignment of the horizon and a star (Polaris, the sun, etc.). The mirrors permitted the image of the sun to be viewed through the eyepiece side by side with the horizon. The instrument also allowed the observer to take into account the pitching and rolling of a ship, making this instrument more accurate than its predecessor. With the development of manufacturing in Europe at this time, the octant's size was reduced to nearly half the size of the Davis Quadrant making this instrument more convenient for sailors. The light paths in the instrument could also be covered with shades, permitting direct observation of the sun and so was useful at any time of the day.

John Hadley

“Hadley’s Octant.” Philosophical Transactions of the Royal Society, vol. 37, p. 147.

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1731

Wikimedia Commons

Public Domain

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